Ball transfer units, sometimes referred to as conveyor ball units, are commonly used in connection with conveyor tracks for the movement or handling of freight, such as the loading and unloading of cargo from an aircraft. Multiple ball transfer units collectively provide a surface over which the cargo may be moved with a minimum amount of friction. Ball transfer units are also utilized on machine tools, such as stamping presses, to transfer the stock through the machining area.
A ball transfer unit, such as the type described in U.S. Pat. No. 5,297,663 to Sundseth, comprises a conveyor ball resting on a plurality of ball bearings in a housing. The conveyor ball and the plurality of ball bearings are located within a mounting shell so as to maintain the position of the conveyor ball and ball bearings within the housing. In addition, a retaining ring is provided to keep the conveyor ball in position on the ball bearings within the mounting shell. The conveyor ball is positioned so as to permit its rotation when material is moved along the conveyor track over the ball transfer unit.
Due to their application, conveyor tracks, and thus ball transfer units, are often subjected to significant forces. Such ball transfer units must be designed to be rugged so as to withstand these loads. Some ball transfer units are designed to allow for limited upward and downward movement of the mounting shell for absorbing such compressive loads on the conveyor ball. For example, the mounting shell and the retaining ring as disclosed in U.S. Pat. No. 5,219,058 are mounted on a helical spring such that the retaining ring may move upward and downward with the conveyor ball within the housing. The '058 patent discloses this movement for the purpose of absorbing compressive loads on the conveyor ball.
An ultimate goal of the ball transfer unit is to provide anti-friction qualities that will improve the operation and efficiency of the conveyor track. Ball transfer units currently known in the art are often subjected to corrosive chemicals, particulate contaminants, and fluids which enter the race of the housing and cause the surface of the conveyor ball to corrode and wear. The corrosion and wear of the conveyor ball can significantly restrict the anti-friction qualities of the ball transfer unit, and thus significantly diminish the efficiency of the conveyor track. To protect the conveyor ball, a seal is commonly used to wipe the ball as it rolls to prevent fluids and contaminants from entering the race. Typically, such a seal would have a close tolerance fit with the outer periphery of the conveyor ball, such as the edge of the aperture described in U.S. Pat. No. 1,963,956 to Craig. This close tolerance fit, however, cannot account for imprecisions in the manufacturing of the ball, uneven wear of the ball which occurs during its service life, or deflection of the ball due to the force of excessive loads. Consequently, corrosive chemicals, particulate contaminants, and fluids manage to pass between such seals and the ball, enter the race, and degrade the anti-friction qualities of the ball transfer unit. In fact, the patentee of the '956 patent described how foreign matter such as dust would accidentally find its way into the race of the unit. Realizing such accidental introduction of foreign matter would occur, said patent provided for an aperture to dispel such matter once it had been worked into the bottom of the race by the ball bearings. This does not, however, preclude the matter from degrading the conveyor ball.
When such seals do manage to prevent the introduction of such chemicals or contaminants from entering the race of the ball transfer unit, the art provides no mechanism for subsequently expelling or eliminating such matter from the exterior of the seal or ball transfer unit itself. The buildup of this matter on the seal of the ball transfer unit or on the ball transfer unit itself could also be detrimental to the operation of the unit in conjunction with the conveyor track.
Furthermore, because of the probable size of the conveyor track and the plurality of ball transfer units that would be used in such a track, it is necessary to design the ball transfer unit so as to minimize the difficulty and inconvenience of replacing a damaged ball transfer unit.
An object of the present invention is to provide a ball transfer unit which substantially alleviates the problems discussed above.
A further object of the present invention is to provide a ball transfer unit for a conveyor track which is able to support significant loads and forces which are commonly involved in the operation of such a ball transfer unit.
A further object of the invention is to provide a ball transfer unit which effectively prevents the introduction of chemicals and other contaminants into the race of the ball transfer unit.
A further object of the invention is to provide a ball transfer unit for a conveyor track which minimizes the difficulty and inconvenience of replacing an individual ball transfer unit in a conveyor track.
A more specific object of the invention is to provide a seal for a ball transfer unit that prevents the introduction of chemicals and other contaminants into the race of a ball transfer unit.